The human aorta contains three different collagen species: Type I, Type III and Type IV. A method has been developed by which human aortic tissues can be pepsinized and fractionally precipitated to yield relative pure fractions of each of these three collagen types. The Type IV collagen constitutes less than 10% of the total present and has unique and unusual solubility properties. However, a new fractionation method has been derived which makes purification of this molecular species now routinely possible. This material is being studied as a stimulant of smooth muscle cell cultures, as an aggregator of platelets and as an antigen. Organ cultures of human and rabbit vessels have been established. Such vessels can be maintained in vitro for up to two weeks in an active biosynthetic state. Biochemical, ultrastructural and autoradiographic studies are being conducted to evaluate synthesis of extracellular materials in vessels which have been subjected to a number of different treatments prior to culture including de-endothelization, exposure to various diets, and elevated pressures. A new protein has been isolated from the cardiovascular tissues which appears to have the capacity to bind calcium. The basis for this binding activity may relate to the presence of an unusual amino acid, gamma carboxyglutamic acid.